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Variable Compression Ratio (VCR) technology has long been recognized as a method of improving Spark Ignition (SI) engine fuel economy. The Pressure Reactive Piston (PRP) assembly features a two-piece piston, with a piston crown and separate piston skirt which enclose a spring set between them. The unique feature is that the upper piston reacts to the cylinder pressure, accommodating rapid engine load changes passively. This mechanism effectively limits the peak pressures at high loads without an additional control device, while allowing the engine to operate at high compression ratio during low load conditions. Dynamometer engine testing showed that Brake Specific Fuel Consumption (BSFC) improvement of the PRP over the conventional piston ranged from 8 to 18 % up to 70% load. Knock free full load operation was also achieved. The PRP equipped engine combustion is characterized by reverse motion of the piston crown near top dead center and higher thermal efficiency.

There is a clear trend towards Hybrid Electric Vehicles (HEV) due to the environmental concerns. On the other hand, with increasing hotel and ancillary loads and replacement of more engine driven mechanical and hydraulic loads with electrical loads, automotive systems are becoming more electric. This is the concept of More Electric Cars (MEC) which necessitates going to a higher voltage such as 42V for conventional cars. Can the evaluation of the 42V MEC smoothly lead to the Hybrid Electric Vehicles (HEV) and More Electric Hybrid Vehicles (MEHV)? In this paper, we investigate the feasibility of 42V & 14+42V electrical power systems for MEHV. Technical issues of such a solution are explored in detail.